AU615756B2

AU615756B2 - Application of an iron-base alloy for powder metallurgical production of parts with high corrosion resistance high resistance to wear as well as high strength and resistance to pressure, in particular in the processing of plastics

Info

Publication number: AU615756B2
Application number: AU36662/89A
Authority: AU
Inventors: Alfred Dr. Kulmburg; Hurbert Dipl.-Ing Lenger; Johann Dipl.-Ing. Stamberger
Original assignee: Boehler GmbH; Boehler GmbH Germany
Current assignee: Boehler GmbH Germany
Priority date: 1988-06-21
Filing date: 1989-06-20
Publication date: 1991-10-10
Anticipated expiration: 2009-06-20
Also published as: AU3666289A; ES2052971T5; PT90925A; AT393642B; DE58902742D1; EP0348380B1; JPH0277556A; EP0348380A1; EP0348380B2; ATA159988A; ATE82595T1; ES2052971T3; JP2583451B2; ZA894703B; PT90925B

Abstract

Use of an iron-based alloy for the production of sintered parts of high corrosion resistance, high wear resistance, high toughness and high compressive strength, in particular for processing plastics, having a composition, in % by weight, chromium 16.0-29.0, molybdenum 0.4-2.5, tungsten 0.3-2.0, vanadium 3.0-10.0, titanium up to 5.0, aluminium up to 1.0, boron up to 0.05, nitrogen 0.01-0.18, niobium up to 5.0, iron and preparation-related impurities as the remainder, the value formed from (% of Cr - 13) + 4.4 x (% of V - 3) + 2 x (% of Nb) + 4.2 x (% of Ti) being greater than 8.8, and the minimum carbon content of the alloy corresponding to the correlation Cmin = 0.3 + [(% of Cr - 13) x 0.06] + [(2 x % of Mo + W) x 0.03] + (% of V x 0.24) + (% of Nb x 0.13) + (% of Ti x 0.25) and the maximum carbon content of the alloy corresponds to the correlation Cmax = 0.7 + [(% of Cr - 13) x 0.06] + [(2 x % of Mo + W) x 0.03] + (% of V x 0.24) + (% of Nb x 0.13) + (% of Ti x 0.25), with the proviso that the matrix has a chromium content of at least 13% after hardening and annealing, and the carbide content is at least 25% by volume, the carbide grain size being less than 14 mu m and at least 5 % by volume of the carbides being in the form of MC carbides.

Description

BUHLER Gesellschaft r.b.H S igned (jU ppa. Dipl.-Ing. Mac-he-5 i.A. Dr. Saurer D eclara N m Nam F B. RICE CO PATENT ATTORNEYS Tis form is suitable for any type off'atent Application, No legalisation required.

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COMMONWEALTH OF AUSTRALIA 41 Patent Act 1952 E S PE CI F I CA T IO0N D 0 CO0M PL ET

(ORIGINAL)

Class Int. Class Application Number Lodged Complete Specification Lodged Accepted Published 9 9* **0 9 is .Priority: 21 June 1988 Related Art ~*,Name of Applicant Address of Applicant BOHLER Ges.m.b.H.

p c-,tfachj 96, A-8605 Austria Kapfenberg, Actual Inventor '9 9 9"I e *9 Dr. Alfred Kulmburg, Dipl.-Ing. Johann Stamberger Dipl.-Ing. Hurbert Lenger F.B. R~ICE CO., Patent Attorneys, 28A Montague Street, BALMAIN. 2041.

Address for Servi--,:: Complete Speci~fication for' he invention entitled: "lApplication of an iron-base alloy for powder metallurqical proauction of parts with high corrosion resistance high resistance to wear as well as high strength and resistance to pressure, in particular in the processing of plastics" The following statement is a full description of this invention including the best method of performing it known to Us:-

V

2 The present invention concerns the usage of an iron-based alloy with special composition as a material for the powder-metallurgical production of parts with hi;' corrosion resistance, high wear resistance, as well as high toughness and compressive strength, such as in plastic moulding dies, machine parts and tools for ch,pless forming processes. In the plastics industry in particular, moulding parts are known to be simultaneously exoosed to chemical and abrasive wear and tear, whereby these parts, due to the mechanical loadings, have to C: °exhibit possibly high material toughness, high compressive :strength and special material homogenity. Such demands are made, for example, on materials for the pressing of fibre-reinforced plastics or filler material containing 15 plastics.

For machines elements, such as feeder screws etc., and also for forming tools and press tools, whfich, In particular, are exposed to corrosive wear and tear, austenitic steels or chrokium steels with a chromium o° 20 content of about 18%, for example, alloys according to DIN eoo material No. 1.4528, are used. Even though these materials show adequate corrosion resistance, the wear o o behaviour is, at least in practical operation, not satisfactory.

In order to improve or increase, respectively, the wear resistance and hardness of the steel, it has also been tried to increase the carbide component of the alloy through higher carbon content.

These steels, such as alloys according to DIN material No. 1.2080 and material No. 1.2379, with a carbon-content of about 2% and a chromium-content of about 12%, do show improved wear resistance, but they are less suitable for corrosive wear and tear, whereby these parts behave anisotropically, due to the possibly unfavourable carbide structure present, whereby they are brittle and

L

-3have a high tendency to fracture and also do nc~t have adequate stability during heat treatment.

It has also been proposed, to use steels, which h av e an extremely wide range in their chemical composition, in particular for the carbon content, the chromium content and the vanadium content, whereby, however, no indication was given, how such an alloy, which showed high corrosion resistance and high wear resistance, together with adequate toughness charcteristics and high compressive strength, had to be composed. Even the experts could not #0 draw any conclusions from it, as to how and by what means a combination of these required material characteristics could be achieved.

00 The present invention seeks to avoid the 0 11 00915 above -mentoned disadvantages and to provide suitable materials, in particular for, say, the plastics -processing 'A industry, which by their special composition in the usage 0 of certain manufacturing processes, show highi corrosion resistance, high wear resistance and high compressive strength with good toughness characteristics, 00 0 0 0 The present invention consists in the use of an 01 00 .0006 iron-Lased alloy in a powder -metallurgical1 process, said "0 alloy having a composition in by weight: DO silicon max. manganese max. f0 sulphur max,. 0.03 phosphorus max. 0.03 al achromium 16.0 -29.0 molybdenum 0.4 tungsten 0.3 vanadium 3.0 10.0 titanium up to aluminium up to nickel max. 0.8 cobalt max. 0,8 4 copper max. boron up to 0.05 nitrogen 0.01 0.18 niobium up to iron and contaminants due to the nature of the process make up the balance, whereby the value, which is formed by (%Cr 13) 4.4 x 3) 2 x 4.2 x (%Ti) is greater than 8.8 and the minimum carbon content of the alloy corresponds to the relation C 0.3 13) x 0.06] x %Mo min W) x 0.03] x 0.24) (%Nb x 0.13) (%Ti x 0.25) and the maximum carbon content corresponds to the 0 :relationship 0: 15 Cma x 0.7 13) x 0.06] x %Mo 000 max 0 0oo W) x 0,03] x 0 74) (%Nb x 0,13) (%Ti x 0.25) wherein the matrix has a c -omium content of at least 13% and the carbide content is least 25. by volume after -t hardening and tempering, whereby the grain size of the 20 carbide is smaller than 14 pm and at least 5% by volume of the carbides are formed as MC-carbides. It is preferred, 00 0o that the alloying components amount to 0 000° chromium 18.0 25.0 molybdenum 0.6 1.7 25 tungsten 0.5 vanadium 3.5 5.6 nitrogen 0.03 0.1 niobium up to titanium up to boron up to 0.03 by weight, whereby in further embodiments, the material shows a niobium content of 0.2 to 3.0 and/or a titanium content of 0.2 to 3.5 and/or a boron content of 0.001 to 0.002.

ki r '1 4a It is also preferred that the alloy has a carbon content in by weight of at least 1.8 and at most 6,2.

It is particularly preferred, if the value, formed by 44 4 4 44 9 44 4 '4 44 4 4 4444 4 4 .4 4 444, 4 4 4 t It- '4 *4 4 144 4 444444 4 .4 :4 Aj1

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I, r -f (%Cr 13) 4.4 x 3) 2 x 4.2 x (Ti) is at least 10.0.

The parts, which are produced according to a powder-metallurgical manufacturing process from the alloy according to the present invention or the material according to the present invention, must in all parts of the matrix show a chromium concentration of at least 13% after hardening and tempering.

Surprisingly, it has been shown that alloys according to the present invention, from a certain minimum value o" o S onwards, which takes into account the concentrations and the respective effect of the mutual interaction of the 0* 0000 carbide-forming elements chromium, vanadium, niobium and titanium and which, in particular, governs the wear o S 15 resistance of the material with certain, narrowly defined Jo 0 carbon concentrations and the use of powder metallurgical manufacturing processes, results in materials, which simultaneously show high corrosion resistance, high wear resistance, high compressive stability and high toughness 20 nd which can be used advantageously, particular for the 0a0* 00 construction of plastic moulding dies, whereby, after 0o00 hardening and tempering, the chromium contents in all regions of the matrix and the proportion, as well as the 0° o composition of the grain size of the carbides can be set according to the present invention.

The following description concerns alloys of the 00 0 present invention and the effect of said alloying elements: o0<o o0 Silicon, as a deoxidizing agent, influences the composition of the oxides and in small concentrations may advantageously affect the polishability of the parts i formed from the alloy.

However, concentrations of more than 1% by weight have an adverse effect in the solidification characteristics and possibly also on the transformation processes during heat treatment. Manganese concentrations

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6 I up to 1% by weight are possibly of importance for sulphur concentrations of up to 0.03% by weight, in order to bind the sulphur as a sulphide and thereby improve the toughness of the material. The effect of phosphorus is embrittlement and in steel should be as low as possible, but always under 0.03% by weight. Chromium is an alloying element, which, from a concentration of 13% by weight onwards in the matrix, gives rise to the corrosion resistance of the material. At the same time, chromium promotes the formation of carbides, which, with carbon at o, .certain carbon activities and in the presence of S' molybdenum and vanadium, forms, apart from M 7

C

3 4 Scarbides, also M 23

C

6 carbides. Therefore, it is important that the steel contains at least 16% by weight o 15 of chromium, at most, a concentration of 29% by weight of SS chromium, because higher chromium concentrations lead to 4o embrittlement of the material. Molybdenum in concentrations of 0,4 to 2.5% by weight and tungsten in concentrations of 0.3 to 2.0% by weight cause a rise in the secondary hardness during heat treatment through the #6 formation of fine carbides and are important for the fine 0 ,4 adjustment of the carbon activity of the alloy. Vanadium, as a strong promoter of the formation of carbides, causes 44 the formation of MC-carbides, in particular with concentrations of more than 0.7 to 3% by weight. Higher concentrations, in particular above 10%, lead to an o< improvement in the wear resistance, though the toughness S of the parts deteriorates significantly. Titanium up to by weight improves the wear resistance of the material, in particular through MC-carbide formation. Due to the formation of nitrides, nitrogen concentrations from 0.01% onwards have the effect of reducing the grain size or prevent grain growth during annealing at high temperatures, respectively, whereby a decrease in the toughness of the alloy is avoided.

i: -I I-i ~CI, 1 7 Furthermore, with nitrogen concentrations of up to 0.18%, the wear resistance, in particular, can be improved. Aluminium, as an element with high affinity for oxygen and high affinity for nitrogen, can be alloyed in concentrations up to 1% by weight for the standardization of low oxygen concentrations in the steel and for the avoidance of grain growth, whereby advantageous effects on the transformation behaviour and the toughness of the material can be achieved.

It was also found that for the setting of the desired a o mechanical properties of the part, a minimum value is required, which is formed by the concentrations of the S0 carbide and nitride-forming elements, such as chromium, tungsten, niobium, titanium and certain active factors of 15 these elelments, whereby an increase in this value causes t an improvement in the wear resistance and the compressive Via, strength, with a slight fall in toughness. Further, it is important that the carbon content is kept within narrow limits, depending on the concentrations and certain active parameters of the carbide-forming elements in the steel, I in order co achieve the desired prope.ties of the parts.

6 .Hereby, on one hand, M 7

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3

M

2 8

C

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C

carbides are formed for matrix hardening and for the achievement of high compressive strength, and MC-carbides for the setting of high wear strength, whereby, on the other hand, the chromium content required for the corrosion resistance of more than 13% is present in all osego parts of the matrix.

Powder-metallurgical manufacture of the parts is essential, because the isotropic properties of the material are substantially improved and the grain sizes of the precipitations or intermetallic phases, respectively, can be kept small.

Carbides with grain sizes of more than 14 um decrease the mechanical properties significantly, in particular the i m A 8 bending strength of the parts. Powder production can occur with all suitable processes, in particular the gas atomization process, after which compacting through warm isostatic pressing and/or hot working of the powder in suitable casings, may be carried out.

The present invention will now be further described by way of an example.

From a melt with the following concentrations in by weight chromium 20.0 molybdenum tungsten 0.6 o* vanadium o nitrogen 0.04 o o 15 and a correspondingly standardized carbon concentration of 1.9, as well as o ilicon 0.3 S9 manganese 0.35 phosphorus 0.012 20 sulphur 0.011 aluminium 0.001 nickel 0.2 S* cobalt 0.1 0o* copper 0.12 9 25 iron and contaminants due to the nature of the 0o o process, to make up the balance, an alloying powder was produced by means of the gas o atomization process.

b" After the powder has been placed into a capsule with °o 30 a diameter of 250 mm and evacuation and gas-tight sealing of the capsule, a hot forming process was carried out at under application of a 6-fold deformation rate.

Following a normalizing process at 880 to 90 0 c and slow cooling, plastic moulding dies were formed from the forged bar. Hereby, the hardness of the material was about 280 i 1 l r

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Is- A 9- HB. Hardening of the parts occurred after heating to a temperature of 1140 0 C and subsequent cooling in a hot-quenching bath, whereby a hardness value of 61 HRc was measured. After tempering to a temperature of 540 0

C,

the hardness of the material was found to be 59 HRc. The average bending strength, measured transversely to the direction of deformation, was 3.5 kN/mm 2 and therefore was significantly above the values that were measured on parts of comparable hardness, which were manufactured by conventional methods. For the determination of the compressive strength, the 0.2% compressive strain was used, whereby a value of 2015 N/mm 2 was measured, The Sz test of the wear resistance of the part was carried out in a grinding wheel test, whereby a steel wheel rotates in a mixture of corundum and water and against which the sample is pressed. The following wear conditions were used: contact pressure of the test piece 30 N material of grinding wheel C ~:oi hardness of gtinding wheel 126 (HViO) width of grinding wheel 15 mm diameter of grinding wheel 168 mm speed of the grinding wheel 50 rpm CIO o sample size 20 x 20 x 8 0 t Al 2 0 3 -sludge: (solid particles/H2O) 4 1 A1203- grain size 0.7 pm.

In the test, a specific wear (relative to a highly wear resistant, but less corrosion resistant material with a composition of 2.3% C, 12.5% Cr, 1.1% Mo, 4.0% V) of o.4* 200% was measured after 100 secs, 128% after 1000 h and °0o '0 30 120% after 10 00 h. The corrosion characteristics of the material were determined in a salt spray test, whereby the corroded surface gave a value of 50% after 480 min. A further test of the corrosion characteristics in acetic acid over a period of 24 hours resulted in a value i of 6.98 g/m 2 h. The metallographic, ft A 10 electron-microscopical and X-ray-analytical tests showed that the carbide content was about 39% by volume, whereby about 10% by volume were present ati l>carbides, with a maximum grain size of 10 urn.

9t 444 4

Claims

1. Use of an iron-based alloy in a powder-metallurgical process, said alloy having a composition in by weight: silicon max. manganese max. sulphur max. 0.03 phosphorus max. 0.03 chromium 16.0 29.0 molybdenum 0.4 tungsten 0.3 vanadium 3.0 10.0 titanium up to aluminium up to 004 0 nickel max. 0.8 cobalt max. 0 .8 copper max. boron up to 0.05 nitrogen 0.01 0.18 niobium up to iron and contaminants due to the nature of the process make up the balance. whereby the value, which is formed by

4.4 x 2 X 4,2 x (%Ti) is greater than 8.8 and the minimum carbon content of the alloy corresponds to the relation Cmiri 0.3 13) x 0.06] x %Mo W) x 0.03] x< 0.24) (%Nb x 0 13) (%Ti x 0.25) and the maxiuim carbon content corresponds to the relationship -12 Cmax 0.7 (%Cr 13) x 0.06] x %Mo W) x 0.03] x 0.24) (%Nb x 0.13) (%Ti x 0.25) wherein, the matrix of the alloy has a chromium content of at least 13% and the carbide content is at least 25% by volume after hardening and tempering, whereby the grain size of the carbide is smaller than 14 pm and at least by volume of the carbides are formed as MC-carbides. 2. The use of an iron based alloy as claimed in claim 1, wherein said alloy has a composition in by weight a a silicon max. 0.6 manganese max, 0.6 sulphur max. 0.015 phosphorus max. 0.02 chromium 18.0 25.0 molybdenum 0.6 1.7 a tungsten 0,5 4 a a vanadium 3.5 5.6 titanium up to aluminium up to a nickel max, a a a cobalt max. copper max, 0.4 boron up to 0.03 nitrogen 0.03 0.1 a a0 niobium up to iron and contaminants due to the nature of the ooa, process make up the balance. 3, The use of an iron-based alloy as claimed in claim 1 or 2, wherein the value, which is formed by (%Cr 13) 4.4 x 3) 2 x 4.2 x (%Ti) 1 13 is greater than 10.0. 4. The use of an iron-based alloy as claimed in any one of claims 1 to 3 wherein, said alloy has a niobium content in by weight of 0.2 to The use of an iron-based alloy as claimed in any one of claims 1 to 4 wherein, said alloy has a titanium content of 0.2 to

6. The use of an iron-based alloy as claimed in any one of claims 1 to 5 wherein, said alloy has a boron content of 0.001 to 0.002.

7. The use of a hardened and tempered iron-based jlloy as claimed in any one of claims 1 to 6 wherein, said alloy is hardened and tempered, whereby the grain size oi °4 carbide formed is smaller than 14 um and at least 5% by volume of the carbides formed as MC-carbides, 8, The use of an iron-based alloy as claimed in any one of claims 1 to 7 wherein, said alloy has a carbon content in by weight of at least 1.8 and at most 6.2.

9. The use of an iron-based alloy as claimed in any one of claims 1 to 8 wherein, said alloy is used as a material for the powder-metallurgical manufacture of plastic moulding dies. The use of an iLon-based alloy substantially as hereinbefore described with reference to the example. 4 4 DATED this 19th day of June 1989. BOHLER Ges.m.b.H Patent Attorneyts for the Applicant: F.B. RICE CO.